This invention relates to the preparation of soft contact lenses for optical correction, based on synthetic hydrated polymers. More specifically, a unique series of crosslinked polyurethane and polyurea-urethane polymer gels is found to be particularly suitable for this purpose. These polymers are formed from high molecular weight isocyanate end-capped prepolymers which are substantially comprised of ethylene oxide units. These hydrophilic polymers are characterized by their biocompatibility and by their exhibiting a unique surface which resists nonspecific protein adsorption.
Numerous polyurethane polymers have been previously identified. Quite a few hydrogel polymers, prepared from various prepolymers, have been prepared and used for widely varying applications. Typically, hydrogels are formed by polymerizing a hydrophilic monomer in an aqueous solution under conditions such that the prepolymer becomes crosslinked, forming a three-dimensional polymeric network which gels the solution. Polyurethane hydrogels are formed by polymerization of isocyanate-end capped prepolymers to create urea and urethane linkages.
Polymer-based soft contact lenses are not new. U.S. Pat. No. 4,259,467 (Keogh et al.) discloses hydrophilic contact lenses prepared from the polymerization of polysiloxane monomers. U.S. Pat. No. 4,113,685 (Holcombe, Jr.) discloses hydrophilic contact lenses prepared from a copolymer of 2-hydroxyethyl methacrylate, isobutyl methacrylate, trimethylolpropane, trimethylacrylate, methacrylic acid, 2,5-dimethyl-2,5-bis-(2-ethyl hexoylperoxy)hexane.
A number of references disclose the use of polyurethane polymers or copolymers. U.S. Pat. No. 3,786,034 (Blair et al.) discloses the use of water absorptive polyurethane polymers of resins of low equivalent weight and high molecular weight and slightly in excess of equimolar ratios of polyisocyanates or urethane linkage precursors for soft contact lenses. U.S. Pat. No. 4,359,558 (Gould et al.) discloses polyurethane diacrylate compositions for contact lenses, and U.S. Pat. No. 4,454,309 (Gould et al.) discloses polyurethane polyene compositions in which the polyene may be a polyacrylate. U.S. Pat. No. 4,255,550 (Gould) discloses the manufacture of contact lenses from polyurethane resins derived from polymers characterized by lactone groups and hydroxyl groups in the polymer backbone.
Prior art hydrogels tend to adsorb proteins from solutions with which they are brought into contact. This is a particular problem in attempting to utilize polymeric hydrogels for health care applications, such as contact lenses, where proteins are omnipresent. The result may be occlusion or clogging of the polymer, clouding, contamination, irritation to adjacent body tissues, or loss of tissue or bodily fluid protein by irreversible adsorption or denaturation.